Varieties are developed to intensify specific characteristics of the plant, or to differentiate the strain for the purposes of marketing or to make it more effective as a drug. Variety names are typically chosen by their growers, and often reflect properties of the plant such as taste, color, smell, or the origin of the variety.[citation needed] Cannabis strains commonly refer to those varieties with recreational and medicinal use. These varieties have been cultivated to contain a high percentage of cannabinoids. Several varieties of Cannabis, known as hemp, have a very low cannabinoid content, and are instead grown for their fiber and seed.

Pure sativas are relatively tall (reaching as high as 4.5 meters), with long internodes and branches, and large, narrow-bladed leaves. Pure indica varieties are shorter and bushier, have wider leaflets. They are often favored by indoor growers for their size. Sativas bloom later than indicas, often taking a month or two longer to mature. The subjective effects of sativas and indicas are said to differ, but the ratio of tetrahydrocannabinol (THC) to cannabidiol (CBD) in most named drug varieties of both types is similar (averaging about 200:1). Unlike most commercially developed strains, indicalandraces exhibit plants with varying THC/CBD ratios.[3] Avidekel, a medical marijuana strain developed in Israel, has a very low content of THC but a high content of CBD, limiting its recreational value but maximizing medical effect.[4]

Sativa is known for being a more of a head high, energizing strain where psychoactivity is more common, whereas indica, is known for being more of a body high that helps pain and also used as a sedative.[5]

The informal designation sativa and indica may have various, controversial meanings. Morphologically, the name sativa designates tall plants with narrow leaves, while indica refers to short plants with wide leaves. Among the marijuana community however, sativa rather refers to equatorial varieties producing stimulating psychoactive effects (THC:CBD [almost equal to] 1), whereas indica -type plants from Central Asia are used for relaxing and sedative drugs (THC:CBD > 1) [8].[6]

There is an increasing discussion whether the existing paradigm of the difference between species adequately represents the variability found within the genus Cannabis.[7][8][9]
There are five chemotaxonomic types of Cannabis: one with high levels of THC, one which is more fibrous and has higher levels of CBD, one that is an intermediate between the two, another one with high levels of cannabigerol (CBG), and the last one almost without cannabinoids.[10]

There has also been a recent movement [11] to characterize strains based on their reported subjective effects. For example, WoahStork has used machine learning algorithms to classify strains into six Distinct Activity groups.[12]

In addition to pure indica, sativa, and ruderalis varieties, hybrid varieties with varying ratios of these three types are common. For example, the White Widow hybrid containing about 60% indica and 40% sativa ancestry. These hybrid varieties exhibit traits from both parental types. There are also commercial crossbredhybrids which contain a mix of both ruderalis, indica or sativa genes, and are usually autoflowering varieties. These varieties are bred mostly for the medicinal cannabis market, since they are not very appreciated by recreational cannabis users because ruderalis varieties are lower in THC and impart a slightly unpleasant taste. “Lowryder” was an early auto-flowering hybrid that retained the flowering behavior of ruderalis plants, while also producing appreciable amounts of THC and CBD. Autoflowering cannabis varieties have the advantage of being discreet due to their small stature. They also require shorter growing periods, as well as having the additional advantage that they do not rely on a change in the photoperiod to determine when to flower.

Breeding requires pollinating a female cannabis plant with male pollen. Although this occurs spontaneously and ubiquitously in nature, the intentional creation of new varieties typically involves selective breeding in a controlled environment.

When cannabis is cultivated for its psychoactive or medicinal properties, male plants will often be separated from females. This prevents the fertilization of the female plants, either to facilitate sinsemilla flowering or to provide more control over which male is chosen. Pollen produced by the male is caught and stored until it is needed.

When a male plant of one strain pollinates a female of another strain, the seeds will be F1 hybrids of the male and female. These offspring will not be identical to their parents. Instead, they will have characteristics of both parents. Repeated breeding results in certain characteristics appearing with greater regularity.

It is impossible for a hermaphrodite to create any male only plants. A hermaphrodite may create female only seeds and hermaphrodite seeds. Also the female only seeds may carry the hermaphrodite trait.[13]

In a retail market that is decriminalised such as in The Netherlands, where wholesale production is illegal but prosecutions are not always enforced because of the contradiction of the law that is recognised by the courts[14], competition puts pressure on breeders to create increasingly attractive varieties to maintain market share. Breeders give their strains distinct and memorable names in order to help differentiate them from their competitors’ strains, although they may in fact be very similar.

Popular strains are incorporated into new hybrids, which often bear a similar name to their parent. This phenomenon has occurred with Haze and Sour varieties, amongst others.

Bedrocan is a medicinal cannabis variety cultivated from a Dutchmedical marijuanaCannabis sativa L. strain, having a standardized content of THC (22%) and CBD (1%). It is currently cultivated by Bedrocan Nederland, Bedrocan Canada and Bedrocan Česká Republika. It was first introduced in 2003 and is dispensed through pharmacies after prescription from a physician.[18]

Charlotte’s Web is a high-cannabidiol (CBD), low-tetrahydrocannabinol (THC) Cannabis extract marketed as a dietary supplement under federal law of the United States.[20][21][22] It is produced by the Stanley brothers in Colorado. It does not induce the psychoactive “high” typically associated with recreational marijuana strains that are high in THC.[23] In September 2014, the Stanleys announced that they would ensure that the product consistently contained less than 0.3% THC.[24] Charlotte’s Web gained national attention when it was used to treat Charlotte Figi’s epileptic seizures.[25][26] Her story has led to her being described as “the girl who is changing medical marijuana laws across America,”[27] as well as the “most famous example of medicinal hemp use”.[28] There is little evidence about the safety or efficacy of cannabinoids in the treatment of epilepsy.[29][30]

Skunk refers to cannabis strains that are strong-smelling and have been likened to the smell of the spray from a skunk. These strains of cannabis are believed to have originated in the United States prior to development by Dutch growers.[40] Just as with other strains of cannabis, skunk is commonly grown in controlled indoor environments under specialized grow lights, or in a greenhouse when full outdoor conditions are not suitable; skunk strains are hybrids of Cannabis sativa and Cannabis indica.[40]

^Tedesco, Laura (December 8, 2014), Why Parents of Children with Epilepsy Are Increasingly Turning to Marijuana, yahoo.com, retrieved February 9, 2016, ‘Charlotte’s Web is high in CBD and low in THC,’ … To many in the medical community, these parents are relying, at best, on shaky science. A 2013 Cochrane review of studies examining CBD as a treatment for epilepsy concluded that, due to the dearth of large, high-quality studies, ‘the safety of long-term cannabidiol treatment cannot be reliably assessed.’